Sky Guides - Helicopters

Prospective SkyGuides In Helicopter Nap of the Earth Flight

Prospective SkyGuides In Helicopter Nap of the Earth Flight

Helicopter pilots make use of nap-of-the-Earth (NoE) flight to increase stealth and mission security.  Such tactical flight, close to the ground and amongst the surrounding obstacles, is characterised by the pilot making continuous corrections in speed, height and heading, guided by a mental model of where his or her aircraft will be in the future.  The pilot uses what can be described as ‘prospective control’ to evolve a safe trajectory, or skyway, based on perception of the aircraft’s changing velocity and direction from instant to instant.  How far into the future this mental model needs to project is a central question for research into vision aids, the answer to which depends on the task being flown and, critically, on the aircraft’s performance and handling qualities.  For NoE tasks, turning through a terrain-gap, stopping in a clearing or climbing over a hill, there is clearly a requirement for an adequate flight safety margin

In engineering terms, the positional states and motion velocity and turn rate describe the flight control task.  The pilot effectively transforms perceived motion in the optical frame of reference into relative motion in the inertial frame of reference and applies feedback regulation to minimise errors between the commanded and perceived motion.  In an alternative, active psychophysics framework, flight control can be described in terms of pilots picking up information generated by motion over terrain and around obstacles, through variables in the optical flow-field from the surfaces in their field of vision.

Progressive Visual Degradations during approach to oil rig

Optical flow rate can, for example, provide the pilot information on ground speed in eye-heights per second or surface slant.  Another optical variable is that which specifies the time to contact or close to an obstacle or surfaces at the current closing rate – tau. Tau provides a temporal scaling of the external environment and, like other flow-field variables, provides pilots with instinctive information about their motion relative to external surfaces.  More recent developments of tau theory have hypothesised that purposeful motion is guided by couplings arising from either external or internal sources.  This hypothesis will feature as a central theme in the research.

General Tau-theory applies to gap closure using any form of sensory input. The pilot picks up information from the visual scene, allowing them to co-ordinate and synchronise motions. This synchronisation is achieved by keeping the Taus of the motion gaps (say X and Y) coupled in constant ratio.

A specific focus will be the potential use head-up displays in civil helicopter operations and the design of tau-based display formats.  Areas of innovation will include:

  • Develop tau theory to include novel intrinsic guides and coupling techniques
  • Apply tau theory to understand how pilots use visual information in visually deprived situations (accident scenarios will be used as a basis)
  • Apply tau theory to understand how pilots use visual information


Current Work

Future Work